Questions about the life proof case for iPhone five
Well, anything using a thicker screen protector like the one on the life proof case is going to impact the overall responsiveness of the touchscreen. Keep in mind that when you put a case like this on, you are a sensually adding an extra layer on top of the screen itself. Though it will work very well with the life proof case on, it does also depend on how hard you tend to touch the screen. If you are a light toucher, it might not be as responsive. however, if you are a more heavy toucher, you probably won't have any issues.
The overall protection when using the case is actually very solid. You should have no issues using the shower when the phone is in the case. Though the volume might be slightly less pronounced due to cushioning over the speaker in order to prevent water from seeping in.
Splash back should not be an issue for you as the case is built to be submerged. in Essence, it does exactly what it is supposed to do. As stated, many of the things you asked about depend on you. The volume may be slightly less loud then you might be used to and the touchscreen responsiveness is also dependent on what kind of user UR.